We have determined the phase behavior of a series of model poly(ethylene)−poly(ethylethylene) (PE−PEE) diblock copolymers with poly(ethylene) block volume fractions (f PE) ranging from 0.25 to 0.46. Four ordered microstructures make contact with the ODT:  spheres arranged on a body-centered cubic lattice (Im3̄m space group), cylinders packed on a hexagonal lattice, a bicontinuous structure of space group Ia3̄d, and lamellae. A fifth ordered phase, tentatively identified as hexagonally perforated layers (HPL), separates the cylindrical and lamellar morphologies at moderate or greater degrees of segregation. Binary blends of f PE = 0.37 and 0.46 diblocks were used to investigate the bicontinuous cubic phase region in greater detail; these experiments indicate that this phase extends as much as 100 °C below the ODT for 〈f PE〉 values in the blend from 0.385 to 0.420.

Orientation correlations in a quiescently quenched, lamellar block copolymer were examined by a combination of depolarized light scattering and transmission electron microscopy. These experiments reveal exponential correlation functions with characteristic lengths that depend on the thermal history of the sample. The correlation lengths obtained from light scattering and electron microscopy are in reasonable agreement. IntroductionMany materials of biological and commercial importance comprise stacks of microscopic layers: biological membranes, metallic alloys, and lamellar phases formed by surfactants and block copolymers. In the absence of external fields, these materials consist of locally ordered, but globally disordered stacks or grains, with concomitant point, line, and wall imperfections. Aspects of these assemblies are well understood due to several decades of theoretical and experimental effort. 1-4 The average layer spacing has been obtained by small-angle X-ray and neutron scattering. Optical microscopy and electron microscopy have been used to investigate the topology of imperfections. A feature of interest that has escaped quantitative analysis is the extent of local coherence of the lamellae. Finite coherence and imperfections are nonequilibrium features, determined not only by the state of the sample but also by its history. Material properties such as stress-strain relationships and permeability are dependent on these features. In this paper, the statistical properties of quiescently quenched block copolymer lamellae were obtained by a combination of transmission electron microscopy (TEM) and depolarized light scattering. These experiments reveal that an exponential function describes the correlation between lamellar orientations at different points in the material. In related studies concerning correlations in disordered and partially ordered media, Levitz et al. have examined density correlations in Vycor glass, 5 while Murray and co-workers have studied bondorientation correlations in two-dimensional colloidal suspensions. 6

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